This proposal investigates novel signaling mechanisms of protein kinase D (PKD) and its relevance to the pathogenesis of prostate cancer. The family of PKD serine/threonine kinases is a novel target of the key second messenger diacylglycerol (DAG) and its pharmacological analogs, phorbol esters. DAG and phorbol esters directly bind PKD at its C1 domain and activate PKD through phosphorylation via protein kinase C (PKC). Aberrant DAG signaling is closely couples to the etiology of many cancers including the prostate cancer. PKD as a novel DAG target has significant prognostic and therapeutic values for these diseases. Substantial evidence from our studies supports a novel role of PKD3, a new member of the PKD family, in prostate carcinogenesis. We have demonstrated progressive nuclear accumulation of PKD3 as well as elevated expression in human prostate tumors, revealing a potential mechanism whereby PKD contributes to the development of prostate cancer. PKD3 promotes prostate cancer cell growth, survival, and migration/invasion, and knockdown of PKD3 inhibits the growth of prostate tumor xenografts in mice. PKD3 signals downstream of PKC5, an oncogenic protein in prostate cancer, and modulates crucial cell growth/survival regulatory pathways including Akt and EKR1/2 in prostate cancer cells. These findings support the crucial role of a constitutively active PKC5/PKD3 pathway in prostate oncogenesis. The proposed studies will further dissect the signaling mechanisms of PKD3 and define its functional impact in the pathogenesis of prostate cancer. If successful, these studies will reveal the potential value of PKD3 as a novel biomarker and therapeutic target for prostate cancer. Ultimately, new strategies may be designed for targeting PKD3 as therapy for prostate cancer as well as other diseases with deregulated DAG signaling. Three specific aims will be tested in this proposal: Specific Aim 1. Determine the role of PKD3 in the pathogenesis of prostate cancer in vivo. Specific Aim 2. Test the hypothesis that the nuclear accumulation of PKD3 as a consequence of constitutively active PKC5/PKD3 is essential for growth, survival, migration/invasion of prostate cancer cells. Specific Aim 3. Determine relevance of PKD3 in acquired phorbol 12-myristate 13-acetate (PMA) resistance and cell proliferation in prostate cancer cells.